Jaws 3-D: over-under 3D projection
Inventors and investors in the field of 3-D have since day one been looking for a way to display the 3-D image in a better, cheaper and mostly in a less obstructing way. This idea has proven itself to be a must over the last century if 3-D cinema is to climb out of the depths of obscurity and cheap-thrill exploitation. The golden egg of 3-D image display would without a doubt be a worldwide glassless cinema / TV system. A system where consumers will not need to purchase new equipment, pay more for their theatre ticket, TV subscription service or DVD and where distributors, broadcasters and theatre owners do not need to make additional investments or have direct costs. So this would be a system that works on current hardware, both in the cinema and at home, or on the up and coming hardware systems like DLP projection and HDTV. However much that means a transitional period of backwards incompatibility, and however much all parties involved agree this is an acceptable sacrifice.
An auto-stereoscopic system is not likely to happen in cinemas, though. S.P. Ivanov devised a perfect one in 1940 for use in the Soviet Union and it worked beautifully, but seating was limited to a few seats in the middle of the theatre. This spelled financial doom for glassless 3-D in cinema.
The best and most practical system ever devised is the polarizing system developed by the Polaroid corporation in 1929. Light travels in both horizontal and vertical waves, so this property can be used to separate the left-eye and right-eye image by means of transmitting one by horizontal light waves and the other by vertical ones. This can be done by using polarizers which let through only one angle of light. Being an optical system, this works perfectly in cinema with its projection through light, but not with television. Only those people with a beamer at home will be able to use this system to view 3-D films. This system was used almost exclusively in the 3-D boom of 1953 and of 1983. Different ways of projecting through these polarizers was used, though, in both years. First, two synchronised projectors and two strips of film were used, later one strip of film with (anamorphic) side-by-side or over-and-under imagery, projected through recombining lens systems.
The field- or frame-sequential system works in different ways for cinema and television, where at the moment it is only used in IMAX theatrically, employing a system of 48 fps film, infrared emitters and LCD glasses responding to these emitters by opening and closing left-eye and right-eye glasses at 48 fps as well. For television, the systems uses even and uneven fields to display the left-eye and right-eye image sequentially, resulting practically in an image that runs at 12.5 fps on PAL and 15 fps on NTSC. This low frame rate and the resulting flicker can cause quite some discomfort with viewers. However, this is the only system useable on current televisions that can display proper 3-D without resulting in ghosting or the need for spinning cameras like in the Pullfrich system.